1-cyclohexyloctane is isomerized on the large pore, bifunctional zeolite catalyst Pt/H-Y. The detailed isomerization mechanism of this naphtene molecule is revealed through a thorough analysis of the numerous isomerization products. It is found that methyl side-chains are generated on the ring of the molecule via a ring contraction-expansion mechanism, which are subsequently transferred to the n-alkyl substituent via methyl shifts. Direct branching of the n-alkyl chain is a much slower process compared to the generation of methyl substituents on the ring.